Dragon Bones added 2 new dungeons, housing storage, and the outfit system.
Summerset added a new zone, a new trial, and jewelry crafting. Battlegrounds became base game, Morrowind (zone) is a DLC, and Warden class in a separate upgrade. It also added daily login rewards.
Wolfhunter - another 2 dungeons
Murkmire - added a new zone, a new 4 man arena. Cyrodiil now has destructible bridges and mile gates, and a few extra outposts. It also had some major balance changes. Passive dodge was replace with AOE damage reduction, sorc and light armor damage shields are now capped at 50% of max health, and most sources of Major Expedition had their duration shortened.